#include<stdio.h>
#include<malloc.h>
void main()
{
	int a[][3]={ 1,2,3,4,5,6,7 };
	int *b;
	int **c;

	b=(int *) a;
	c=(int **)a;

	for(int i=0;i<3;i++)
		for(int j=0;j<3;j++) 
			printf(" %d %d",*b++,*c++);
}

    printf(" %u %u %u %u \n",b,c,b+1,c+1);
After adding this statement before the for loop:

Output:
 1245020 1245020 1245024 1245024
 1 1 2 2 3 3 4 4 5 5 6 6 7 7 0 0 0 0

#include<stdio.h>
#include<malloc.h> /* Non-standard header that isn't used, remove it. */
void main() /* main() has a return type of int */
{
   /* Here you declare a two-dimensional array that holds a total of nine
      elements, but you only initialize seven of them. The last two gets
      whatever the compiler puts there, often 0 if you compile in debug mode.
      Also, one usually puts a pair of {} around each row. If you had bothered
      to compile with warnings turned on you would've noticed the compiler 
      complaining about this, among other things. */
   int a[][3]={ 1,2,3,4,5,6,7 };
   int *b;
   int **c;

   b=(int *) a;
   c=(int **)a;

   /* Using a nested loop here is ridicolous since
      you only use the postincrement-operator in
      the call to printf(). Use a single loop instead
      and move the loop-variable declaration to the top
      of the main() function to be compliant with older
      C standards. */
   for(int i=0;i<3;i++)
      for(int j=0;j<3;j++) 
         printf(" %d %d",*b++,*c++);

   /* Since main() has a return type of int, you should
      return 0 here. */
}

#include <stdio.h>

int
main(void)
{
   int a[][3]={ {1,2,3},{4,5,6,},{7,8,9} };
   int *b = (int *)a;
   int **c = (int **)a;
   int i = 0;
   int num_elements = sizeof(a) / sizeof(int);

   for(i = 0; i< num_elements; ++i)
      printf("*b = %d *c = %d\n", *b++, *c++);

   return 0;
}

*b; /* Yields an int, because b is of type pointer-to-int. */
**c; /* Yields a-pointer-to-int, because b is of type pointer-to-pointer-to-int. */